Operating brakes serve for holding an elevator cage of an elevator or holding a step belt of an escalator in a specific position. They can also be used for retarding a moved elevator cage or a moved step belt. In cases of emergency such as, for example, in the case of power failure the brake systems are designed so that they brake with “maximum braking force.” The maximum braking force is fixed in relevant standards. Operating brakes are usually electromechanical brake systems. The at least one brake thereof is pressed by means of spring elements against the friction surface, which is to be braked, of a brake disc, a brake drum or a support means (cable or belt). For release of the brake use is made of an electromagnet which is suitable for overcoming the spring force of the spring elements. The foregoing explanations can also apply analogously to moving walkways with a plate belt.
Even when the brake shoe is pressed by the effective surface thereof against the friction surface by a constant spring force the friction resulting therefrom and thus the deceleration during the braking process substantially change. Influences such as the temperature during the brake use, contamination of the effective surface and the friction surface, changes in the surface thereof and in the structure due to preceding use of the brake and the like lead to a strongly fluctuating braking performance. This can lead to unsatisfactory braking behavior, which due to the selected setting of the brake can represent a compromise between the bandwidth of the attainable braking travel and the maximum reasonable placing of load on the user.
Safety brakes are triggered usually only in cases of emergency and have the task of fixing moved components, such as an elevator cage, counterweight, a step belt or a plate belt, as rapidly as possible. Safety brakes can be arranged at the elevator cage and/or at the counterweight or act on a support means connecting the elevator cage with the counterweight. Triggering of a braking process takes place through an electrical or mechanical signal of a speed limiter. In elevator standards passed by regulators, deceleration values or negative acceleration values of the elevator cage, which are not to be exceeded, are stipulated for braking processes. Very high negative acceleration values usually arise between the friction surface and the effective surface shortly before transition from a sliding friction to an adhesive friction. The negative acceleration values usually run progressively in an unfavorable manner. A constant deceleration value of, for example, −3 m/s2 could be perceived as significantly unpleasant.